1. Field of the Invention
The present invention relates to a vacuum booster for use in a brake system of an automotive vehicle. More particularly, the present invention is directed to a method of manufacturing a vacuum booster housing including an annular plate for reinforcing the portion of the wall of the body of the housing to which the brake master cylinder is secured as generally disclosed in co-pending, commonly assigned, U.S. patent applications, Ser. Nos. 306,738 and 306,739, both filed Sept. 29, 1981.
2. Description of the Prior Art
Conventional vacuum boosters for use in brake systems of automotive vehicles include a housing comprising a shaped, sheet metal body and a cooperating shaped sheet metal cover secured together to form a vacuum chamber. The vacuum booster housing is secured to the vehicle by means of bolts through holes in the cover. The brake master cylinder is secured to the housing by means of bolts through the body.
In conventional installation, the brake master cylinder is attached to an annular wall portion of the body of the booster housing by a plurality of bolts disposed in spaced holes in the annular wall portion with the head of the bolts inside the housing and the threaded, shaft portion of the bolts passing through the holes to the outside of the housing. Nuts secure the brake master cylinder to the shaft portions of the bolts extending outside of the housing.
The annular wall portion of the body to which the brake master cylinder is secured is subjected to the substantial load applied to the master cylinder from the booster. The body of conventional booster housings, therefore, have conventionally been manufactured of thicker sheet metal material to give the annular wall portion to which the master cylinder is attached sufficient strength to withstand the load.
Recently, in order to improve the fuel economy of automotive vehicles, efforts have been made to reduce the weight of the components of such vehicles. A significant weight saving may be achieved by reducing the thickness of the sheet metal material used to form the body portion of the booster housing.
Accordingly, it has been proposed to provide an annular reinforcing plate interposed between the inner surface of the annular wall portion of the body and the seating faces of the head portions from the bolts to which the master cylinder is secured to provide sufficient strength for withstanding the loads imposed on the master cylinder without using thicker sheet metal material to form the body. Co-pending, commonly assigned, U.S. patent application Ser. Nos. 306,738 and 306,739, both filed on Sept. 29, 1981, are directed to booster housings incorporating such annular reinforcing plates.
The installation of a reinforcing plate within the booster housing increases the complexity of the manufacturing process. One known method for manufacturing a booster housing with a reinforcing plate is to secure the bolts to the reinforcing plate and then, in a second step, weld the reinforcing plate to the annular wall portion of the booster housing to which the master cylinder is secured. These additional steps increase the manufacturing costs of the booster housing and, therefore, the overall vehicle.
Another known method of installing a reinforcing plate in a booster housing, as shown in FIG. 1, requires forming the seating face of the head portion 1a of bolt 1 with an annular projection 1b coaxial with the shaft portion 1c. In this method, the seating face of the head portion 1a having the annular projection 1b is disposed in holes in the reinforcing plate 3 and the head portion 1a of bolt 1 is electrically insulated from contact with reinforcing plate 3 by a layer of electrical insulation 2. The bolt 1 is then projection welded to the body 4 such that shaft portions 1c project through holes 4a in body 4, and the seating face of the head portion 1a is secured to the inner surface of the body 4. This known method increases the manufacturing cost by requiring the step of applying the insulation layer 2 to the inside face of the reinforcing plate so as to permit projection welding of the seating face of the head portion 1a to the inner surface of body 4. Furthermore, in this method the reinforcing plate 3 is not directly secured to either the body 4 or the head portion 1a of the bolt 1 presenting the possibility that the reinforcing plate may become loose and rattle.
The present invention provides a method for manufacturing a booster housing incorporating an annular reinforcing plate wherein the reinforcing plate is secured to and between the annular wall portion of the body and the seating face of the head of the bolt in a one-step operation. The one-step operation substantially reduces the cost of manufacturing of the booster housing, and the secured attachment of the reinforcing plate to both the annular wall portion and the seating face of the bolt head provides additional security against displacement of the reinforcing plate.